title: Cross-Shear in Metal-on-Polyethylene Articulation of Orthopaedic Implants and its Relationship to Wear.
abstract: Wear of polyethylene (UHMWPE) is dependent on cross-shear. The aim of the present study was: 1) to develop a theoretical description of cross-shear, 2) to experimentally determine the relationship between cross-shear motion and UHMWPE wear using a wheel-on-flat apparatus, and 3) to calculate the work it takes to remove a unit volume of wear for the use in advanced computational models of wear. The theoretical description of cross-shear has been based on the previously reported finding that cross-shear is maximal when movement occurs perpendicular to fibril orientation. Here, cross-shear is described with a double-sinusoidal function that uses the angle between fibril orientation and velocity vector as input, and maximum cross-shear occurs at 90° and 270°. In the experimental part of the study, friction and wear of polyethylene were plotted against increasing sliding velocity vector angles, i.e. increasing cross-shear. It was found that wear intensified with increasing cross-shear, and wear depth could be predicted well using the double-sinusoidal function for cross-shear (r2=0.983). The friction data were then used to calculate the work to remove a unit particle by integrating the frictional force over the directional sliding distance. Using the wear volumes, determined for both longitudinal and perpendicular motion directions, the work to remove a unit volume of material wasqy= 8.473 × 108J/mm3andqx= 1.321 × 108J/mm3, respectively. Hence, 6.4 times more work was necessary to remove a unit wear volume in the direction of principal motion (i.e. along the molecular fibril orientation) than 90° perpendicular to it. In the future, these findings will be implemented in computational models to assess wear.
authors.affiliation: Department of Orthopedic Surgery, Rush University Medical Centre, Chicago (IL), USA.
authors.forename: T
authors.initials: T
authors.lastname: Schwenke
authors.forename: M A
authors.initials: MA
authors.lastname: Wimmer
keywords: Cross-Shear; Polyethylene; Unit Work; Wear Factor; Wear Model